1. Field of the Invention
The present invention relates to a Network Entry and Initialization process of a terminal, and more particularly to a method for scheduling broadcast messages to reduce a time consumed for carrying out the network entry and initialization process of terminals.
2. Discussion of the Related Art
In a broadband wireless access system, whenever each terminal is powered on, misses its cell, or moves from one cell to another cell, it performs a network entry and initialization process of terminals.
FIG. 1 is a flow chart illustrating the network entry and initialization process.
Referring to FIG. 1, a terminal scans a downlink (DL) channel, and establishes synchronization with a base station (BS) at step S110. The terminal receives the step S110 by receiving a preamble, a downlink MAP (DL-MAP), and a Downlink Channel Description) (DCD) message from the base station (BS).
If the terminal has established synchronization with the base station (BS), it obtains uplink parameters (i.e., Tx parameters) from the Uplink Channel Descriptor (UCD) message at step S120.
Then, the terminal performs a ranging process, and performs an automatic adjustment process at step S130.
Next, the terminal negotiates basic capabilities with the base station (BS) at step S140.
If the basic capability negotiation is completed, the base station (BS) authorizes a subscriber station (SS), and performs a key exchange at step S150. The step S150 can be carried out only when the base station (BS) and the subscriber station (SS) support the authorization policy, but it may be unnecessary.
Next, the subscriber station (SS) performs a registration process in the base station (BS) at step S60.
A step S170 for establishing IP connectivity, a step S180 for establishing ‘time of day’, and a step S190 for transferring operational parameters may be carried out according to either first information indicating the support or non-support of the BS and SS or second information indicating selection of the SS.
FIG. 2 is a flow chart illustrating a downlink synchronization process of the terminal.
FIG. 2 shows detailed operations of the step S110 for performing downlink synchronization with the base station (BS) in the network entry and initialization process.
Referring to FIG. 2, the subscriber station (SS) searches for a frame in an arbitrary channel (e.g., an i-th channel) at step S210, and begins to search for a preamble until detecting a valid downlink signal at step S220.
If the preamble is detected at step S220, the subscriber station (SS) establishes physical synchronization of frequency and time using the detected preamble. Also, if the subscriber station (SS) receives a DL-MAP message at step S230, it establishes MAC synchronization at step S260, and starts operating T1 and T12 timers at steps S240˜250.
In the meantime, if the subscriber station (SS) does not detect the preamble or does not receive the DL-MAP, it goes to the next channel at step S235, and searches for a frame at step S210. Namely, the subscriber station (SS) repeats the steps S235 and S210 until detecting the preamble or receiving the DL-MAP.
FIG. 3 is a flow chart illustrating a process for maintaining the downlink synchronization of FIG. 2.
Referring to FIG. 3, if the subscriber station (SS) has successfully received DL-MAP and DCD messages within a lost DL-MAP interval or a T1 interval at step S310, it maintains downlink synchronization and initializes a corresponding timer at step S320. In this case, ‘T1’ can be represented by the following equation 1:T1=5×DCD interval maximum value  [Equation 1]
In Equation 1, ‘DCD interval maximum value’ is set to 10 seconds. In this case, if the subscriber station (SS) does not receive any of corresponding messages until a timer associated with each message expires, the subscriber station (SS) starts searching for a new downlink signal at step S330.
FIG. 4 is a flow chart illustrating a method for allowing a terminal to acquire uplink-associated parameters.
FIG. 4 shows detailed operations of the step S120 for receiving uplink-associated parameters in the network entry and initialization process.
Referring to FIG. 4, the subscriber station (SS) establishes downlink synchronization with the base station (BS) at step S410, and waits for a UCD message to acquire uplink-associated information.
If the subscriber station (SS) does not receive the UCD message until the T12 timer expires, or if the received UCD message is improper for the subscriber station (SS), the SS retries to perform a first process of the network entry and initialization process. Namely, the SS retries to perform a downlink channel search process S480. In this case, ‘T12’ can be represented by the following equation 2:T12=5×UCD interval maximum value  [Equation 2]
In Equation 2, ‘DCD interval maximum value’ is set to 10 seconds.
If the subscriber station (SS) receives the UCD message before the T12 timer expires at step S420, it waits for an UL-MAP message for a selected channel. In this case, if the uplink channel is available at step S430, the subscriber station (SS) acquires uplink parameters at step S440, resets the T12 timer, and maintains uplink information.
FIG. 5 is a flow chart illustrating a process for maintaining uplink-associated parameters of FIG. 4.
Referring to FIG. 5, if the subscriber station (SS) has successfully received UL-MAP and UCD messages within a given time (i.e., lost UL-MAP interval or T12 interval) at step S510, it maintains valid uplink information, and resets the T12 timer at step S520.
In the meantime, it the subscriber station (SS) has not received the corresponding messages until timers associated with individual messages have expired, the SS determines that uplink-associated information is invalid, and deletes uplink channel parameters at step S530.
Thereafter, the subscriber station (SS) starts detecting a new downlink signal at step S540.
FIG. 6 is a conventional flow chart illustrating a network entry and initialization process.
In more detail, FIG. 6 shows a flow chart of messages generated while steps before the SS ranging are performed. In this case, it is assumed that DL-MAP and UL-MAP messages are transmitted to each frame during a frame duration interval of 20 ms. Also, it is assumed that a DCD or UCD transmission interval is set to a maximum value of 10 s.
The base station (BS) transmits a preamble, a DL-MAP, a UL-MAP at intervals of 20 ms at steps S601 and S602. Although the mobile station (MS) is powered on at step S603 and receives other messages other than the preamble, it is unable to recognize the received messages at step S604.
The mobile station (MS) enters its synchronization status at step S606, after receiving the preamble and the DL-MAP at step S605. Then, the mobile station (MS) waits to receive the DCD message from the base station (BS) at step S607. The mobile station (MS) receives the DCD message at step S608 and obtains downlink-associated parameters. Then, the mobile station (MS) waits to receive the UCD message from the base station (BS) at step S609.
The mobile station (MS) receives the UCD message at step S610, obtains uplink-associated parameters at step S611, and waits for information of resources allocated for the initial ranging at step S612.
If the mobile station (MS) obtains the resource information from the UL-MAP message at steps S613 and S614, it transfers a CDMA code according to the initial ranging procedure at step S615.
As described above, in order to perform the ranging process, the mobile station (MS) must sequentially read a plurality of messages (i.e., preamble, DL-MAP, DCD, UCD, and UL-MAP) in the order of preamble→DL-MAP→DCD→UCD→UL-MAP. If the DCD or UCD transmission interval is set to a maximum time of 10 s, the above-mentioned conventional art may be ineffective from the viewpoint of a time consumed for carrying out the network entry and initialization process of mobile stations.